Polymer-fibre prepreg, a method for the preparation thereof as well as the use of said prepreg

ABSTRACT

The invention relates to a method for the preparation of the fibre product pre-impregnated with a polymer (prepreg) where the method includes: a) coating the fibres with a powder comprising at least one polymer and optionally an agent having the ability to initiate the polymerization reaction of the polymer, b) adding to the composition obtained in step a) a solvent possessing the ability to dissolve the polymer but lacking the ability to initiate the polymerization reaction of the polymer, and c) evaporating the solvent. Alternatively, the polymer (optionally including the initiating agent) can first be dissolved in the solvent after which the fibres are contacted with the solution thus obtained and the solvent is evaporated. The surface of the fibres is preferably treated so as to facilitate the bonding of the polymer to the fibres, whereafter the surface treated fibres are coated with the polymer powder. The invention relates further to a novel prepreg, a method for the manufacture of fibre reinforced composite based on the use of the prepreg, the novel composites and their use.

FIELD OF THE INVENTION

The present invention relates to a method for the preparation of a fibreproduct pre-impregnated with a polymer (prepreg). The invention relatesfurther to a novel prepreg, a method for the manufacture of fibrereinforced composite based on the use of said prepreg, the novelcomposites and their use.

BACKGROUND OF THE INVENTION

The publications and other materials used herein to illuminate thebackground of the invention, and in particular, cases to provideadditional details respecting the practice, are incorporated byreference.

Dental devices made from polymers are prone to fracture in the oralconditions. For instance, it is well documented that a removable denturecan fracture after the denture has been worn for some years, (1-4).Consequently, an ideal reinforcement of a denture should be used both inthe fabrication of a new denture and in repairing of an old denture. Thepolymer devices and constructions in dentistry have traditionally beenreinforced with metal inclusions of the polymer (5-7). The effect of themetal inclusions in the strength of the polymer device or constructionis, however, inadequate. Attempts have been made to develop apolymer-fibre composite which can easily be used as reinforcement ofdentures. Before the date of the present invention, no fibre-compositeproducts fulfilling the requirements of the clinical dentistry and thedental laboratory technology have been achieved, even though one fibreribbon product exists on the market for use in dentistry (Ribbond®,Ribbon Inc., Seattle, Wash., U.S. Pat. No. 5,176,951).

Known polymer-fibre composites for prosthetic dentistry have been madeby dipping the fibre bundle, ribbon or weave in methylmethacrylate (MMA)monomer or in a mixture of polymethylmethacrylate (PMMA) powder and itsmonomer (MMA). Composites made by this method are, however, not suitablefor use in dentures because of the following shortcomings:

1) inadequate adhesion between the PMMA and the fibres, especially withPMMA to be used in denture repairing, i.e. autopolymerizing PMMA (8),

2) inadequate impregnation of fibres with PMMA (9-11),

3) spreading of the fibres to undesired regions of the denture duringcompression moulding of the PMMA (12),

4) difficult handling of the fibres in the dental laboratory (13), and

5) mechanical irritation of the oral soft tissues due to the protrudedfibres on the denture surface (14).

Attempts have also been made to manufacture a pre-impregnated fibrebundle with a polymer (which is called a polymer-fibre prepreg). Threegeneral methods for the manufacture of such thermoplastic polymer-fibreprepregs have been reported (15):

1) an in situ polymerization method, which is a resin injection methodwhereby the monomer is incorporated into a fibrous preform,

2) a film stacking method in which layers of fibres are laminatedbetween layers of polymer film, and

3) a powder coating method in which fibres are impregnated with polymerpowder which is then melted.

These methods have, however, some shortcomings in terms of dentalrequirements. The in situ polymerization, even though it can be usedwith PMMA, results in a composite having polymerization shrinkage voidsin the structure, wherein said voids will be filled with saliva and oralmicrobes. The film stacking method yields a composite with poor degreeof impregnation (i.e. the fibre bundle is not sufficiently impregnatedby the polymer). The insufficient degree of impregnation will also causevoids in the structure of the composite. The powder coating methodincludes melting of the polymer powder. This method results in a prepregof a dense structure which is difficult to plasticize before the usageby dissolving the polymer. Consequently, any of the methods used ingeneral plastic industry to produce fiber composites are not suitablefor use in fabrication or repairing of dentures.

OBJECT AND SUMMARY OF THE INVENTION

The requirements imposed by clinical dentistry and dental technology ona prepreg useful in dentistry reinforcement are the following:

1) the prepreg must be easy to form into the shape of anatomicalstructures of the oral cavity, i.e. the prepreg should be plastic atroom's temperature when used in denture fabrication or repairing,

2) the prepreg must retain its shape to allow the covering of theprepreg with unfilled (i.e. fibre free) polymer,

3) the polymer of the prepreg should polymerize simultaneously with thesurrounding polymer,

4) the polymer matrix should react chemically with the surroundingpolymer, irrespective of whether it is a heat-curing polymer or anautopolymerizing polymer, and

5) the fibres of the prepreg should adhere to heat-curing polymer aswell as autopolymerizing polymer.

One object of the invention is a prepreg fulfilling the aforementionedrequirements 1) to 5).

Another object of the invention is the use of said prepreg in themanufacture of fibre reinforced composites. Said composites are suitablefor use in any technical field, particularly in the dental or medicalfield.

Thus, according to one aspect of the invention a method is provided forthe preparation of a fibre product pre-impregnated with a polymer(prepreg). Said method comprises either

i)

a) coating the fibres with a powder comprising at least one polymer andoptionally an agent having the ability to initiate the polymerizationreaction of said polymer,

b) adding to the composition obtained in step a) a solvent possessingthe ability to dissolve said polymer but lacking the ability to initiatethe polymerization reaction of said polymer, and

c) evaporating the solvent, or

ii)

a) dissolving a powder comprising at least one polymer and optionally anagent having the ability to initiate the polymerization reaction of saidpolymer into a solvent possessing the ability to dissolve said polymerbut lacking the ability to initiate the polymerization reaction of saidpolymer, and

b) contacting the fibres with the solution obtained in the foregoingstep, and

c) evaporating the solvent.

Although the prepreg can be manufactured in the form of a continuous webit is in many fields of use preferable to manufacture the prepregreadily shaped into its desired form. In this case the compositionobtained in step a) is added to a mould before the solvent is added.After the evaporation the finished prepreg is removed from the mould.

According to a preferred embodiment, the surface of the fibres has beentreated so as to facilitate the bonding of the polymer to the fibres,whereafter the surface treated fibres are coated with the polymerpowder. Preferably, an agent facilitating the bonding of the polymer tothe fibres has been applied onto the fibre surface before the fibres arecoated with polymer powder.

According to another aspect the present invention provides a porousprepreg comprising of fibres and a polymer wherein said polymer ispresent between the individual fibres and has been distributed betweenthe fibres as a solution from which the solvent has been evaporated.

In a particularly preferable prepreg the fibre is a glass fibre, thepolymer is polymethyl methacrylate (PMMA), ethyleneglycoldimethacrylate(EGDMA), 2,2-bis 4-(2-hydroxy3-methacroyloxy)phenyl!-propane (BIS GMA),or hydroxy-ethylenemethacrylate (HEMA), and a silane compound,preferable gamma-methacryloxypropyl-trimethoxy-silane, has been appliedonto the surface of the fibre.

According to yet another aspect the present invention provides a methodfor the manufacture of a fibre reinforced composite based on the use ofthe prepreg according to this invention. Said method comprising thesteps of

adding a plasticizer to the optionally pre-formed prepreg,

shaping the plasticized prepreg into the desired form,

embedding the prepreg into the plain polymer of the composite, or into amixture of said polymer and the monomer, and

allowing the polymer of the prepreg to polymerize simultaneously withthe plain polymer of the composite.

The reinforced composite can be used as such or, alternatively, be usedas starting material for the manufacture of blocks of desired shape.Thus, a dental composite can e.g. be machined into dental restorationsand dental and medical implants.

According to another preferred embodiment, the polymer of the prepreg isthe same as the unfilled polymer of the composite.

The invention further provides a fibre reinforced composite comprising aprepreg according to this invention. Said prepreg has been plasticizedby wetting with a monomer, shaped into the desired form and embeddedinto the plain polymer of the composite, and the polymer of said prepreghas been allowed to polymerize simultaneously with the plain polymer ofthe composite.

Said composite can be used in any technical application. It is, however,particularly suitable for use in medical or dental constructs such asprosthodontic, orthodontic or orthopaedic appliances; removable dentureframeworks, removable denture clasps or precision attachments; permanentor temporary fixed prostheses including tooth and implant supportedprostheses; dental or medical implants; rooth canal fillings ofendodontically treated tooth; posts, cores, fillings or crowns of thetooth, mouth guards, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C demonstrate the use of the prepreg in the repairing of acomplete denture,

FIGS. 2A and 2B show two examples of fiber orientation in repaireddentures (FIG. 2A is a complete denture and FIG. 2B is an upper partialdenture), and

FIG. 3 shows the flexural properties of a GF-PMMA composite.

DETAILED DESCRIPTION OF THE INVENTION

Suitable fibres for use in this invention are either inorganic ororganic fibres. The choice of fibre depends highly on the technicalfield in which the fibre reinforced composite shall be used. Fibresalready tested in dentistry as reinforcement of dentures include E-glass(electrical glass) fibres (10), S-glass (high strength glass) fibers(16), carbon/graphite fibres (12, 17, 18), aramid fibres (19) andultra-high-modulus polyethylene (8, 13, 20-23). The black colour of thecarbon/graphite fibres make them less suitable for dental use. Organicfibres have been reported to cause inadequate adhesion to dental dentalpolymers (8). It seems therefore that glass fibres best fulfill thecosmetic and adhesive requirements for dental use.

The fibres can occur in various forms. As examples can be mentionedrovings, woven rovings, woven mats, chopped strand mats, whiskers or asfibre particles (fillers). The choice of fibre product depends on theintended use of the composite. Mixtures of the various fibre forms canalso be used.

The polymer of the prepreg can be any polymer. For medical and dentaluse a thermoplastic polymer material is preferred. Preferably, thepolymer of the prepreg is the same as the polymer surrounding theprepreg in the finished composite. A preferable polymer for use indentistry is polymethyl methacrylate (PMMA), either heat-curing orautopolymerizing PMMA. Heat-curing PMMA is polymerized on water bath attemperatures in the range of 70° to 100° C. The polymerization isinitiated by an initiator such as benzoyl peroxide (24). Heat-curingPMMA can also polymerized by microwave energy. Autopolymerizing PMMA ispolymerized at lower temperatures (35° to 50° C.) than heat-curing PMMAand therefore a chemical compound, such as dimethylparatoluidine, isrequired to activate the initiator of the reaction (24). Among otherpreferable polymers can be mentioned e.g. ethyleneglycoldimethacrylate(EGDMA), 2,2-bis 4-(2-hydroxy-3-methacroyloxy)phenyl!propane (BIS GMA),polyethyleneterephtalateglycol (PETG), poly1,4-cyclohexylendimethyleneterephtalateglycol (PCTG),hydroxyethylenemethacrylate (HEMA) or the like.

The proportion between the amount of fibres and polymer shouldpreferably be chosen so as to give good porosity of the prepreg afterthe solvent has been evaporated. High porosity is advantageous becauseit enables an easy penetration of the prepreg by the plasticizer. Whenglass fibres and PMMA are used, the best porosity is obtained when equalamounts of fibres and polymer are used.

The surface of the fibre can optionally be prepared to facilitate thebonding of the polymer to the fibre either physically or chemically,e.g. by use of an agent. The choice of the agent facilitating thebonding of the polymer to the fibres (i.e. the coupling agent) dependson the fibres and polymer matrix used. In dentistry, common couplingagents for improving the adhesion between the glass fibres and PMMA aresilanes. A particularly preferred silane compound isgamma-methacryloxypropyltrimethoxysilane (MPS). Adhesion between carbonfibres and the polymer matrix can be improved by oxidative orirradiation methods as well as with silane compounds. Polyethylenefibres can be made more adhesive to the polymer matrix e.g. by plasmaetching of the fibre surface. The results obtained thereto have,however, been rather poor (21).

According to a preferred embodiment of the present invention, thecoupling agent is precured onto the fibre surface before the fibre iscontacted with the polymer. This enables the use of heat-curing polymersas well as autopolymerizing polymers. According to known methods, thecuring of the silane compound occurs simultaneously with thepolymerization of the heat-curing PMMA. There are no reports onsuccessful use of silanes for improving the adhesion betweenautopolymerizing PMMA and glass fibres.

The initiator of the polymerizing reaction is e.g. added either to thepolymer material of the prepreg or to the plasticizer used to plastizethe prepreg before its use. The initiator can be any suitable knownpolymerizing initiator. Most common initiators are peroxides, e.g.benzoyl peroxide.

The solvent used in the preparation of the prepreg can be any solventhaving the ability to dissolve the polymer material but lacking theability to initiate the polymerization reaction thereof. Tetrahydrofuran(THF) is an example of a suitable solvent. The dissolution of thepolymer material and subsequent evaporation of the solvent results in avery good polymer impregnation of the fibre product, which in turn, aswill be disclosed in the examples, results in excellent strengthproperties of the finished composite. The solvent should preferableevaporate rather quickly because this facilitates a porous structure ofthe material in the prepreg.

As plasticizer to be used to plasticize the prepreg can be used amonomer, either the monomer of the polymer powder included in theprepreg, or a different monomer. Preferably the same monomer is used. Incase the polymer is PMMA the monomer will thus be MMA.

The invention is illustrated by the following examples. In the examplesthe invention is explained in terms of its preferred embodiments andapplications in prosthetic dentistry even though the invention also hasother medical and technical applications.

Example 1

Preparation of the prepreg

E-glass fibres (Ahlstrom, Karhula, Finland) in continuous unidirectionalroving form were cleaned by 1.5 mol/l sulphuric acid (H₂ SO₄), washedwith distilled water and then dried for 48 hours at +22° C.

The surface of the fibres was treated withgamma-methacryloxypropyltrimethoxysilane (MPS) (A174, Union CarbideChemicals, Versoix, Switzerland) for improving the adhesion of thepolymer (PMMA) onto the fibres. The dilute MPS (30% MPS, 70% methanol)was precured to the glass fibre surface at +100° C. for two hours.Additionally, commercially surface-treated glass fibres can be used.

The silane treated glass fibres were coated with dental heat-curingpolymethylmethacrylate (PMMA) powder (Pro Base Hot, Ivoclar, Schaan,Liechtenstein) which included benzoyl peroxide as initiator of thepolymerization reaction. The weight of PMMA powder used was equal to theweight of the glass fibres.

A desired amount of powdered glass fibres were placed into a mouldhaving a cavity corresponding to the shape of the prepreg. The powderedfibres were wetted with tetrahydrofuran (THF), a solvent which dissolvedthe PMMA but which did not initiate the polymerization reaction of thedissolved PMMA. In this step the dissolved PMMA bonded the individualfibres together to form a rigid prepreg of predeterminated shape. Thesolvent (THF) was allowed to evaporate. Finally the prepreg was removedfrom the mould and packed for future use.

Another method to fabricate the prepreg is to dissolve a desired amountof PMMA into the THF, and dip the fiber rowing or weave in the mixtureor pull the roving or weave through the mixture. The ratio PMMA to THFshould be optimized to produce porous glass fiber--PMMA prepreg whichcan easily be wetted and plasticized with the MMA when the prepreg isused.

A prepreg based on autopolymerizing PMMA (Pro Base Cold, Ivoclar,Schaan, Liechtenstein) was manufactured in the same way as describedabove.

Example 2

The use of the prepreg as a reinforcement in denture manufacture

An acrylic resin based denture was made from heat-curing PMMA usingcompression moulding technique. The weak regions of the denture werereinforced with the prepreg from Example 1 as follows:

1) After trial packing of PMMA into a denture mould a concavity waspressed into the PMMA dough by using as space-maker a plastic strip ofthe same size as the prepreg.

2) The prepreg was plasticized by wetting it with the monomer of theheat-curing PMMA and placed into the concavity of the acrylic resindough.

3) The final packing of the acrylic resin dough was carried outaccording to usual methods in dentistry (25).

4) The polymerization of the PMMA of the prepreg occurred on water bathsimultaneously with the polymerization of the PMMA dough. The finalproduct thus obtained was a denture comprising an orientated continuousfibre reinforcement coated with a layer of unfilled PMMA.

Example 3

The use of the prepreg in denture repairing

A fractured denture on a dental cast was shaped for repairing asdescribed in the dental literature. Furthermore (see FIG. 1A-1C), agroove 10 of the same size as a prepreg 11 made of autopolymerizing PMMAand glass fibres was ground into the desired region of the denture. Theprepreg 11 was plasticized (FIG. 1C) by wetting with the monomer of theautopolymerizing PMMA and placed into the groove of the denture. Thegroove was then filled with autopolymerizing PMMA which was allowed topolymerize on water bath simultaneously with the polymerization of thePMMA of the prepreg. A repaired denture reinforced with orientatedfibres was thus obtained (see FIG. 2A-2B).

Example 4

The use of the prepreg as frame material of a removable denture

A prepreg was plasticized with the monomer of the polymer matrix. Thenthe prepreg was placed on the dental cast covering the region of theframework. The prepreg was positioned so as to give a fibre directionorientated against the predicted fracture line of the denture. Thesurface of the prepreg was coated with PMMA powder to cover the fibreswith unfilled PMMA. Alternatively, the surface of the prepreg could becoated with a mixture of PMMA powder and MMA liquid (i.e. PMMA dough).The cast was placed into the curing unit for the polymerization of thePMMA. After curing a composite frame was obtained. Said composite framecan be used as a conventional metal frame in the manufacture of aremovable denture.

Example 5

The use of the prepreg as a removable denture clasp

A prepreg, made into the shape of a denture clasp and into the colour ofthe tooth, was plasticized by the monomer of the polymer matrix (PMA).The plasticized prepreg was placed onto the desired region on the dentalcast and it was bonded to the extension base of the removable denture.The prepreg was coated with tooth coloured PMMA powder beforepolymerization in the curing unit. Alternatively, the prepreg could becoated with tooth coloured PMMA dough before polymerization.

Example 6

The use of the prepreg in the fabrication of permanent, semipermanent ortemporary fixed prosthesis

The prepreg comprising of colourless or tooth coloured PMMA (oralternatively polybutylmethacrylate or polyethylmethacrylate or thelike) was plasticized by the monomer of the polymer matrix. Theplasticized prepreg was placed into a silicon mould of the fixedprosthesis which had been partly filled with the PMMA dough. Theplasticized prepregs were then covered with the PMMA dough, and themould was placed on the gypsym cast of the abutment teeth. After curingthe PMMA, the fixed prosthesis was finished with the normal dentallaboratory procedures.

The fixed prosthesis consists of either unidirectional glass fiberreinforcement which increases the strength of pontics and their jointsto crown units, and additionally of glass fiber weave reinforcement, orshort fibre reinforcement, which enhances the strength of the crownunits and the fixed prosthesis.

Example 7

Properties of the fibre composites obtained

The methods described in prior art, i.e. dipping the fibre bundle into amixture of PMMA powder and its monomer, give a degree of impregnation(amount of dental PMMA/amount of continuous unidirectional E-glassfibres) varying from 0.4 to 0.8. The degree of impregnation was lowerfor fibre rovings of higher specific amounts of fibres. The degree ofimpregnation of the composites made of continuous E-glass fibres andPMMA by using prepregs according to the present invention was 0.91 forheat-curing PMMA and 0.98 for autopolymerizing PMMA. Furthermore, thedegree of impregnation was not affected by the specific fibre amount ofthe fibre roving.

Flexural properties of the unidirectional glass fiber reinforced dentalPMMA composite fabricated with the method described in prior art, andaccording to the present invention are shown in Table 1 and FIG. 3. Thetest specimens of the aforementioned test had a fibre concentrationwhich could be easily used in the fabrication method of prior art andaccording to the present invention.

For the glass fibre reinforced removable partial dentures according topresent invention, the fatigue resistance against the bending caused bythe simulated force of the mastification (150N occusal force on 300 msintervals in water at +37° C.) was 15 times higher than that of thetraditional metal wire reinforced denture. The impact strength of theglass fibre reinforced dental PMMA according to the present inventionwas 70 kJ/M² measured by a Charpy-type impact tester (WPM Leipzig,Leipzig, Germany) which is considerably higher than that of the metalwire reinforced PMMA. The occlusal force required to fracture a threeunit fixed partial denture made from dental PMMA was 91N. By reinforcingthe three unit bridge with the prepregs according to this invention, theresistance of the bridge against the occlusal force increased to 350N.

The convertion of MMA to PMMA in the prepregs of glass fiber reinforcedPMMA was as high as in the unreinforced PMMA tested by measuring theresidual MMA release from the composite(high-performance-liquid-chromatography method, in accordance with theISO 1567 standard). Water sorption and solubility of glass fiberreinforced PMMA were also in accordance with ISO specification.

                  TABLE 1                                                         ______________________________________                                        Flexural strength (MPa) and flexural modulus (GPa)                            of autopolymerizing PMMA and unidirectional GF-PMMA                           composite fabricated according conventional technique and                     according to the new prepreg technique (three-pont loading                    tests in accordance with ISO 1567 standards).                                                  Flexural                                                                            Flexural                                                                strength                                                                            modulus                                                ______________________________________                                        Unreinforced PMMA   89.1   2.83                                               GF-PMMA composite with                                                                           231.2   7.12                                               conventional technique                                                        GF-PMMA composite with                                                                           335.0   12.56                                              prepreg technique                                                             ______________________________________                                    

It will be appreciated that the methods of the present invention can beincorporated in the form of a variety of embodiments, only a few ofwhich are disclosed herein. It will be apparent for the specialist thatother embodiments exist and do not depart from the spirit of theinvention. Thus, the described embodiments are illustrative and shouldnot be construed as restrictive.

REFERENCES

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8. Vallittu P. K. Ultra-high-modulus polyethylene ribbon asreinforcement for autopolymerizing polymethyl methacrylate. A shortcommunication. Dent Mater, in press.

9. Grave A. M. H., Chandler H. D., Wolfaardt J. F. Denture base acrylicreinforced with high modulus fibre. Dent Mater 1985; 1:185-7.

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I claim:
 1. A method for the preparation of a prepreg comprising a fibreproduct pre-impregnated with a polymer, said prepreg being porous andeasy to shape at room temperature after the addition of a plasticizer,wherein the method comprises eitheri)a) coating fibres with a powdercomprising at least one polymer and optionally an agent having theability to initiate a polymerization reaction of said polymer, b) addingto the composition obtained in step a) a solvent possessing the abilityto dissolve said polymer but lacking the ability to initiate thepolymerization reaction of said polymer, and c) evaporating the solvent,or ii)a) dissolving a powder comprising at least one polymer andoptionally an agent having the ability to initiate a polymerizationreaction of said polymer into a solvent possessing the ability todissolve said polymer but lacking the ability to initiate thepolymerization reaction of said polymer, and b) contacting the fibreswith the solution obtained in the foregoing step, and c) evaporating thesolvent.
 2. The method according to claim 1 wherein the compositionobtained in step i) a) is added to a mould before the solvent is addedthereto.
 3. A method for the preparation of a prepreg comprising a fibreproduct pre-impregnated with a polymer, said prepreg being porous andeasy to shape at room temperature after the addition of a plasticizer,wherein the method comprises eitheri)a) coating fibres with a powdercomprising at least one polymer and optionally an agent having theability to initiate a polymerization reaction of said polymer, b) addingto the composition obtained in step a) a solvent possessing the abilityto dissolve said polymer but lacking the ability to initiate thepolymerization reaction of said polymer, and c) evaporating the solvent,or ii)a) dissolving a powder comprising at least one polymer andoptionally an agent having the ability to initiate a polymerizationreaction of said polymer into a solvent possessing the ability todissolve said polymer but lacking the ability to initiate thepolymerization reaction of said polymer, and b) contacting fibres withthe solution obtained in the foregoing step, and c) evaporating thesolvent, wherein a surface of the fibres is treated so as to facilitatebonding of the polymer to the fibres, whereafter the surface treatedfibres are coated with the polymer powder.
 4. The method according toclaim 1, wherein the fibres comprise a glass fibre.
 5. A method for thepreparation of a prepreg comprising a fibre product pre-impregnated witha polymer, said prepreg being porous and easy to shape at roomtemperature after the addition of a plasticizer, wherein the methodcomprises eitheri)a) coating fibres with a powder comprising at leastone polymer and optionally an agent having the ability to initiate apolymerization reaction of said polymer, b) adding to the compositionobtained in step a) a solvent possessing the ability to dissolve saidpolymer but lacking the ability to initiate the polymerization reactionof said polymer, and c) evaporating the solvent, or ii)a) dissolving apowder comprising at least one polymer and optionally an agent havingthe ability to initiate a polymerization reaction of said polymer into asolvent possessing the ability to dissolve said polymer but lacking theability to initiate the polymerization reaction of said polymer, and b)contacting fibres with the solution obtained in the foregoing step, andc) evaporating the solvent, wherein the polymer is selected from thegroup consisting of polymethyl methacrylate,ethyleneglycoldimethacrylate, 2,2-bis -propane, orhydroxyethylenemethacrylate, and wherein the agent facilitating thebonding of the polymer to the fibres is a silane compound which has beencured onto the fibres at elevated temperature.
 6. A method for themanufacture of a fibre reinforced composite wherein a prepreg is used,said prepreg comprising a fibre product pre-impregnated with a polymer,wherein said polymer is present between the individual fibres and hasbeen distributed between the fibres as a solution from which the solventhas been evaporated, said prepreg being porous and easy to shape at roomtemperature after the addition of a plasticizer, wherein the methodcomprises eitheri)a) coating fibres with a powder comprising at leastone polymer and optionally an agent having the ability to initiate apolymerization reaction of said polymer, b) adding to the compositionobtained in step a) a solvent possessing the ability to dissolve saidpolymer but lacking the ability to initiate the polymerization reactionof said polymer, and c) evaporating the solvent, or ii)a) dissolving apowder comprising at least one polymer and optionally an agent havingthe ability to initiate a polymerization reaction of said polymer into asolvent possessing the ability to dissolve said polymer but lacking theability to initiate the polymerization reaction of said polymer, and b)contacting fibres with the solution obtained in the foregoing step, andc) evaporating the solvent, said method for the manufacture of a fibrereinforced composite comprising the steps ofadding a plasticizer to saidprepreg, which optionally can be pre-formed shaping the plasticizedprepreg into a desired form, embedding the prepreg into the plainpolymer of the composite or into a mixture of said polymer and themonomer, and allowing the polymer of the prepreg to polymerizesimultaneously with the plain polymer of the composite.
 7. The methodaccording to claim 6 wherein the composite obtained in a further step ismachined into one or more desired blocks or into desired form.
 8. Themethod according to claim 6 wherein the plasticizer is the monomer ofthe polymer used in the prepreg.
 9. The method according to claim 6,wherein the polymer of the prepreg is the same as the plain polymer ofthe composite.
 10. The method according to claim 5, wherein said silanecompound comprises gamma-methacryloxypropyltrimethoxysilane.
 11. Themethod according to claim 1, wherein said solvent possessing the abilityto dissolve said polymer but lacking the ability to initiate thepolymerization reaction of said polymer is tetrahydrofuran.
 12. Aprepreg which is porous and easy to shape at room temperature after theaddition of a plasticizer, said prepreg comprising fibres and a polymerwherein said polymer is present between the individual fibres and hasbeen distributed between the fibres as a solution from which the solventhas been evaporated.
 13. The prepreg according to claim 12 wherein theporous further comprises an agent having the ability to initiatepolymerization reaction of said polymer.
 14. The prepreg according toclaim 12 wherein the fibres are in the form of a roving, woven roving,woven mat, chopped strand mat, short fibres, a whisker or particleformed, or a mixture of the aforementioned.
 15. The prepreg according toclaim 12, wherein the surface of the fibres has been treated so as tofacilitate the bonding of the polymer.
 16. The prepreg according toclaim 12, wherein the fibres comprise a glass fibre, the polymer isselected from the group consisting of polymethyl methacrylate,ethyleneglycoldimethacrylate 2,2-bis-propane andhydroxy-ethylenemethacrylate; and a silane compound has been appliedonto a surface of the fibres.
 17. A fibre reinforced compositecomprising a prepreg which is porous and easy to shape at roomtemperature after the addition of a plasticizer, said prepreg comprisingfibres and a polymer wherein said polymer is present between theindividual fibres and has been distributed between the fibres as asolution from which the solvent has been evaporated,wherein said prepreghas been plasticized by wetting with a monomer, shaped into a desiredform and embedded into the plain polymer of the composite, and thepolymer of said prepreg has been allowed to polymerize simultaneouslywith the plain polymer of the composite.
 18. A composite according toclaim 17 in the form of medical or dental constructs selected from thegroup consisting of prosthodontic, orthodontic and orthopaedicappliances; removable denture frameworks, removable denture clasps;precision attachments; permanent fixed prostheses; temporary fixedprostheses; dental implants; medical implants; root canal fillings of anendodontically treated tooth; posts, cores, fillings and crowns of thetooth; and mouth guards.
 19. The prepreg according to claim 16, whereinsaid silane compound comprises gamma-methacryloxypropyltrimethoxysilane.